Bleedback valve for lift truck hoist cylinders



Dec. 13, 1960 J E OLSON 2,964,021

BLEEDBACK VALVE FOR LIFT TRUCK HOIST CYLINDERS Filed Jan. 13, 1958 2 Sheets-Sheet 1 BY JOHN E. OLSON BUCKHORN,CHEATHAM 8. BLO RE ATTORNEYS J. E. OLSON Dec. 13, 1960 BLEEDBACK VALVE FOR LIFT TRUCK HOIST CYLINDERS Filed Jan. 13, 1958 2 Sheets-Sheet 2 INVENTOR.

JOHN E. OLSON BUCKHORN,CHEATHAM & BLORE RESERVO/R ATTORNEYJ United tes Patent BLEEDBACK VALVE FOR LIFT TRUCK HOIST CYLINDERS John E. Olson, Portland, 0reg., assignor, by mesne assignments, to Hyster Company, a corporation of Nevada Filed Jan. 13, 1958, Ser. No. 708,679

8 Claims. (Cl. 121-46) This invention relates to a free lift cylinder unit of an industrial lift truck, and to certain improvements therein.

In some free lift cylinder units, such as the type" disclosed in the patent to Ptak 2,634,587, there is a completely enclosed chamber between certain of the cylinders that is not at any time supplied with hydraulic fluid under pressure, and thus may be considered as a dead chamber. The cylinders defining this chamber move relative to one another during the operation of the cylinder unit, and as an incident to this movement, the volume of the chamber is varied or changed. A breather device is provided in the Ptak cylinder unit to allow the escape of air from the chamber when the volume of the chamber decreases, and allow ingress of air into the chamber when the volume of the chamber increases, thus to permit ready relative movement of such cylinders.

The disadvantage of this construction is that hydraulic fluid, that is oil, unavoidably leaks into the chamber, and this oil is ejected through the breather device when the chamber volume decreases. This oil runs down the sides of the cylinder unit and falls on the floor on which the truck is being operated, which is objectionable for various reasons not necessary to recite. For convenience, the oil in the chamber will be called leakage" oil.

The main object of the invention is to provide a free lift cylinder unit of the general type described above which is provided with a device which allows the chamber to breathe to permit ready relative movement of the cylinders defining the chamber, but which device conducts the leakage oil expelled from the chamber back to the reservoir of the hydraulic system of the truck instead of allowing it to be deposited on the surface on which the truck is being operated.

A further object is to provide a cylinder unit having a device of the type described above, which device has a conduit means for conducting the leakage oil back to the reservoir, the conduit means being so constructed that there is no possibility of such conduit means becoming entangled with the moving parts of the cylinder unit or of the associated structure and thus being damaged.

Various other objects of the invention will be apparent from the following description taken in connection with the accompanying drawings wherein:

Fig. 1 is a rear view of the free lift assembly of a lift truck showing a bleeder valve device of the present invention applied to the assembly;

Fig. 2 is a horizontal section, on an enlarged scale, taken along line 2--2 of Fig. 1, better showing the man nor of mounting the bleeder valve in place;

Fig. 3 is a fragmentary view in elevation showing the separation of the bleeder valve upon upward movement of the inner uprights relative to the outer uprights;

Fig. 4 is a diagrammatic view of the free lift cylinder unit and the bleeder valve, the view showing the bleeder valve on a much larger scale than the cylinder to better illustrate the operation of the valve;

Fig. 5 is a view similar to Fig. 4 but showing a subsequent stage of the operation, with the two main parts of the valve separated; and

Fig. 6 is a fragmentary view showing one stage of the operation of the bleeder valve. 1

Referring to the accompanying drawings, Fig. 1 shows a pair of fixed outer uprights 11 movably receiving a pair of inner uprights 13 in a conventional fashion not necessary here to set forth and not shown. A free lift cylinder unit 15 of the type disclosed in my copending application entitled Free Lift Truck, Serial No. 543,822, filed October 31, 1955, is operable through the medium of the chains 17 to raise the load carriage 18 of the truck, which is fragmentarily shown, up to the top of the inner uprights 13, and then to raise the inner uprights and the carriage together. This is described in my copending application. An upper cross brace 19 and a lower cross brace 21 connect the inner uprights 13.

Each chain 17 is anchored at 23 at one end to the carriage 18 then extends upwardly over a large sheave 25 at the top of the cylinder unit 15 and then downwardly under a smaller sheave 27 then upwardly where it is anchored to a flange 28 on the upper end of the cylinder unit.

There is a bleeder valve device or assembly of the present invention provided for the cylinder unit and the device includes a bleeder valve composed of two main parts. an upper part 29 and a lower part 31. The upper part 29 is connected by a conduit 33 to the cylinder unit 15, to communicate with a dead chamber therein as will be more fully explained hereinafter. The lower part of 31 is connected by a conduit 35 to the reservoir of the hydraulic system of the truck, as will be presently apparent.

Referring to Figs. 1 and 2, the upper valve part 29 is connected by a bracket 43 to the crosspiece 19, and therefore is effectively connected to the inner uprights 13. The lower valve part 31 is connected by a bracket 47 to one of the outer uprights 11. The valve parts 29 and 31 are separable from one another so that when the inner uprights 13 move upwardly relative to the outer uprights 11, the upper valve part 29 is carried upwardly by the inner uprights 13 to separate it from the lower valve part 31, as shown in Fig. 3. However, so long as there is no movement between the uprights, the valve parts will remain engaged and thus in an operable open position.

Referring to Figs 4 and 5, the cylinder unit 15 is disclosed in more detail and includes a large outer cylinder 51, an intermediate cylinder 53 and an inner cylinder 55 which, in effect, is a plunger. Referring to Fig. '1, the plunger 55 is mounted at its lower end in fixed relation to a crosspiece 57 of the outer uprights 11 whereas, the outer cylinder 51 is connected at its upper end, such as by a bracket assembly 58, to the inner uprights 13 for movement therewith. Thus, the outer cylinder 51 and the inner uprights 13 move in unison, and therefore the upper valve part 29 which is mounted on the inner uprights is disposed infixed relation with respect to the outer cylinder 51 as indicated by the dotted line 59 in Figs. 4 and 5. It also follows that the lower valve part 31, which is mounted on the outer uprights, is disposed in fixed relation with respect to the plunger 55 as indicated by the dotted line 60 in Figs. 4 and 5.

Sheaves 25, previously mentioned, are mounted on the bracket assembly 58, referred to above, and sheaves,

27 are mounted on the lower end of the intermediate cylinder 53. The flange 28, previously mentioned, forms the upper end of the outer cylinder 51.

Referring to Fig. 4, a pump 61 takes oil from a reservoir 63 and pumps it through a' suitable conduit 65' into the lower end of the plunger 55 to first cause a down-y Patented Dec. 13, 1960 I ward movement of the intermediate cylinder 53, as shown in dotted lines in Fig. 4, this movement raising the carriage 18 through the medium of the chains 17 at a rate twice that of the intermediate, cylinder, but leaving. the inner uprights and the outer uprights stationary.

The. intermediate cylinder has acornbination stop and seal 67 engaging the outer cylinder, and the outer cylinder has a similar seal at 69 engaging the intermediate cylinder. These two; cylinders and the seals 67 and 69 provide a, dead chamber 71 which is never supplied with hydraulic fluid. However, oil does leak past the seal 67 into the chamber.

Thus upon downward movement of the; intermediate.

cylinder relative to the outer cylinder, the. volume of chamber 71 is described and some of the leakage oil and part of the air in the chamber are forced outwardly into the conduit 33 and. through the open valve 15 and through the conduit 35 into the reservoir 63. Thus ready movement and operation of the free lift cylinder are permitted, without allowing the oil in chamber 71 to escape and drop on the floor.

After the intermediate cylinder reaches its lowermost position and the seals 67 and 69 are disposed in engagement, the further supply of hydraulic fluid under pressure from the pump 61 causes the outer cylinder 51 and the intermediate cylinder 53 to move upwardly in unisonas indicated in Fig. 5, raising the inner uprights 13 and the load carriage. This upward movement of the outer cylinder 51 causes a separation of the valve 29, 31 as shown in Fig. 5. The valve is constructed to close automatically when the parts 29 and 31 are separated, but sincethere is no relative movement between the cylinder 51 and 53, until the valve parts re-engage, the volume of the dead chamber 71 remains constant until the valve is again open.

The valve is specially constructed. so that there is no time at which the valve is cracked. That is, the valve is constructed so that the valve isclosed before the separation of the valve parts, instead of concurrently therewith, so that there is no escape of oil from the valve at the time the valve partsare being separated or while they are separated.

Referring to Fig. 4, the upper valve part 29 is of tubular construction and contains an annular seal 81 resting against a shoulder 83 and clamped thereagainst by an insert 85 threaded into the lower. end of the member 29. The insert 85 is also of tubular construction and has an internal diameter slightly greater than that of the internal diameter of the seal 81 when the seal is compressed for a reason to be explained. The insert 85 has a flared lower end, as shown at 87, to guide the lower part 31 of the valve into the insert.

Pressed toward the upper face of the annular seal 81 by a spring 89 is a valve element 91 which in the Fig. 4 position of the parts is held in spaced relation from the seal by the upper end of the lower valve part 31. Thus oil and air are permitted to pass through the valve by passing into the ports at 95 formed in the upper end of the valve part 31 and down through an internal passage 97 formed in such valve part. The upper end of the valve part 31 sealingly engages the inner wall of the seal 81 to prevent leakage.

As the cylinder moves from its Fig.4 to its Fig. 5 position, the valve part 31 is withdrawn from the valve part 29. As shown in, Fig. 6', the parts are so dimensioned that the valve element 91 is, in its closed position againstthe seal, 81 while the ports 95 are still closed by the inner wall of such seal. Thus the valve 15 is effectively closed to the passage otfiuid vthenethrough well before the valve part 31. iswithdrawn; from the valve part 29. Thus the valve-isnot cracked? at. any time and. thus there is no drippage of roilrufrom, the valve when the valve parts are separated.

As clearly shownin Fighj, the valve parts 29 and 31 are entirely separated, butwill again. e engagedwhen the cylinder returns ot e Fist 5 p sition of the parts.-

Again, the ports will be sealed first by the annular washer 81 and then the valve element 89 will be raised to open the valve, so that there will be no danger of leakage.

Fig. 2 shows that the inner upright 13 is slightly narrower, that is, not quite as wide, as the outer upright, but this is of no importance since the invention may be obviously readily applied to uprights which are of the same size.

During the movement of the cylinders 51 and 53 from the Fig. 5 back tov the Fig. 4 position, the volume of the dead chamber 71 will increase. Air may be drawn 'from the reservoir during this operation.

It is pointed out that the separate valve construction of the present invention means that there are no long loops of hose to become entangled in the moving parts of the lift assembly and thus be damaged.

Having described the invention in what is considered to be the preferred embodiment thereof, it is desired that it be understood that the invention is not to be limited other than by the provisions of the-following claims.

I claim:

1. In an industrial lift truck mast structure, a pair of relatively movable mast sections, a multi-cylinder means for effecting such. relative movement, one of the cylinders moving in unison with one of the mast sections, conduit means extending to said one cylinder, said conduit means including a telescopic coupling having a first part on said one mast section and a second part on another mast section. which has relative movement with respect to said one mast section, means, mounting said coupling parts on their respective. mast sections in positions to engage one another when said one and said another mast sections are inone relationship with respect to one another and to be separatedfrom one another when the just-mentioned mast sections are in a different relationship with respect to one another, said mounting means providing for automatic re-engagement of said coupling parts with one another when said mast sections return to said one relationship, and valve means for closing off the flow of fluid through at least one portion of said conduit means when said coupling parts are separated.

2. In an industrial lift truck mast structure, a first mast section and a second mast section movable upwardly relative to said first mast section, a multi-cylinder means for efiecting movement of said second mast section, one of the cylinders of the multi-cylinder means moving in unison with said second mast section, conduit means extending to said one cylinder, said conduit means including a telescopic coupling having a first part on said first mast section and another part on said second mast section, means fixedly mounting said coupling parts on their respective mast sections in positions to engage one another when said mast sections are in one relationship with respect to one another and to be separated from one another Whensaid mast sections are in a difierent relationship with respect to one another, said mounting means holding said coupling parts in alignment with one another when said coupling parts are separated to provide for automatic reengagement of said coupling parts when said mast sections return to said one relationship, and valve means operated by relative movement between said coupling parts to close otf flow through at least one portion of said conduit means.

3. A lift structure having a multi-section extensible mast and a multi-section extensible cylinder unit, one of the cylinders of the cylinder unit being movable in unison with one of the. movable mast sections, conduit means connected to said one cylinder, said conduit means having a telescopic coupling including an outer part in fixed relation to said one mast section and an inner part in fixed relation to a secondrelatively movable mast section, seal. ingmeansin said outer part engageable with said inner part, and a movableflow control valve element in said.

outer part engageable with said sealing means when said coupling parts are separated and being separated from said sealing means when said coupling parts are engaged.

4. A lift structure of the type having a multi-section extensible cylinder unit, conduit means connected to a movable cylinder of said unit, said conduit means including a telescopic coupling including an outer part in fixed relation to said movable cylinder and an inner part below said outer part and in fixed relation to another cylinder so that said coupling parts automatically reengage after being separated, and valve means for closing off the flow of fluid through at least one portion of said conduit means when said coupling parts are separated.

5. A lift structure as in claim 4 in which said inner part effects opening of said valve means when said parts are together and closing of said valve means when said inner part separates from said outer part.

6. A lift structure as in claim 5 in which the valve means are biased toward closed position and the inner part engages the valve means to open the same and disengages from the valve means to enable the valve means to close.

7. A lift structure of the type having a multi-section extensible cylinder unit, conduit means connected to a movable cylinder of said unit, said conduit means including a telescopic coupling including an outer part in fixed relation to said movable cylinder and an inner part below said outer part and in fixed relation to another cylinder so that said coupling parts automatically reengage after being separated, sealing means in said outer part engageable with said inner part, and a movable flow control valve element in said outer part engageable with said sealing means when said coupling parts are separated and being separated from said sealing means when said coupling parts are engaged.

8. A lift structure having a multi-section extensible mast and a multi-section extensible cylinder unit, conduit means connected to one of the movable cylinders, said conduit means having a telescopic coupling including an outer part in fixed relation to a movable mast section and an inner part in fixed relation to a second mast section, sealing means in said outer part engageable with said inner part, and a movable flow control valve element in said outer part engageable with said sealing means when said coupling parts are separated and being separated from said sealing means when said coupling parts are engaged.

References Cited in the file of this patent UNITED STATES PATENTS 1,112,631 Longtin Oct. 6, 1914 1,383,209 Iftiger June 28, 1921 2,390,702 Gail et a1 Dec. 11, 1945 2,433,119 Hansen Dec. 23, 1947 2,548,528 Hansen Apr. 10, 1951 

